Synthesis of alcohols via a rhodium-catalyzed hydroformylation-reduction sequence using tertiary bidentate amine ligands

Article abstract of DOI:10.1002/adsc.201200053

The synthesis of alcohols from aromatic olefins is described using a rhodium-catalyzed hydroformylation-reduction sequence with the assistance of a tertiary diamine ligand. The alcohols are produced in excellent branched to linear ratios and in good to excellent isolated yields. In all cases no aldehyde product, from hydroformylation, or alkyl product, from olefin reduction, was detected. Copyright

Full text of DOI:10.1002/adsc.201200053

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DOI: 10.1002/adsc.201200053
Synthesis of Alcohols via a Rhodium-Catalyzed Hydroformylation–
Reduction Sequence using Tertiary Bidentate Amine Ligands
Lawrence L. W. Cheung,a Giuseppe Vasapollo,a,b and Howard Alpera,*
a
Centre for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa, 10 Marie Curie, Ottawa,
Ontario, K1N 6N5, Canada
Fax : (+1)-613-562-5871; phone (+1)-613-562-5800 ex. 5189; e-mail: howard.alper@uottawa.ca
Department of Material Science, University of Salento, Via Arnesano, 73100 Lecce, Italy
b
Received: January 19, 2012; Revised: April 5, 2012; Published online: && &&, 0000
Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/adsc.201200053.
Abstract: The synthesis of alcohols from aromatic hyde product, from hydroformylation, or alkyl prod-
olefins is described using a rhodium-catalyzed hydro- uct, from olefin reduction, was detected.
formylation–reduction sequence with the assistance
of a tertiary diamine ligand. The alcohols are pro-
duced in excellent branched to linear ratios and in Keywords: alcohols; carbonylation; diamine; hydro-
good to excellent isolated yields. In all cases no alde- formylation; reduction
Introduction
or other nitrogen heterocycles[8] that result from re-
acting the intermediate aldehyde[9] are often the goal
The direct synthesis of alcohols from olefins using of the research rather than the aldehyde itself. The
syngas (carbon monoxide and hydrogen) through use of nitrogen ligands in hydroformylation reactions
a two-step hydroformylation–reduction sequence re- is rather uncommon,[10] however it has been shown
mains a challenge. There have been many transition that they can facilitate the formation of alcohols.[11]
metal catalyst systems that have been developed to Beyond simply mono-substituted olefin hydrocarbons,
make alcohols from olefins, including Pd,[1] Ru,[2] there have not been many applications of nitrogen co-
Rh,[3] and Co.[4] Rhodium-catalyzed systems remain ordinating ligands for the synthesis of alcohols from
the most popular because of their high catalytic activi- olefins using
a
hydroformylation–reduction se-
ty. A major problem in producing alcohols from ole- quence.[11] We now report a highly selective alcohol
fins is the lack of reaction selectivity, many side prod- synthesis from olefins using a rhodium-catalyzed pro-
ucts being produced including reduced olefins, n and cess that employs a tertiary diamine ligand.
i aldehydes/alcohols and mixtures of all components.
The industrial process for making alcohols from ole-
fins is currently a two-step process, whereby the alde- Results and Discussion
hyde product is first isolated from the hydroformyla-
tion reaction. A separate second step is needed to Our initial testing began using 1.0 mmol of styrene
reduce the aldehyde to the alcohol product. A one- and the following conditions: 2.5 mol% RhClACHTUNGTRENNUNG[COD]
pot sequence would be much more attractive because dimer, 10 mol% N,N,N’,N’-tetramethyl-1,4-diamino-
it would streamline the process to yield alcohols by butane, H2 and CO gas (1.38 MPa each), and 3 mL of
hopefully lowering the reaction time, labour and over- THF as the solvent, at room temperature. These con-
all cost.
ditions furnished the branched alcohol exclusively but
In general there are many more rhodium/phosphine only in 6% yield. In addition there were no signs of
catalyst systems that produce aldehydes through hy- any olefin reduction product or hydroformylation al-
droformylation,[5] as opposed to catalytic systems that dehyde product. Additional screening ensued which
yield alcohols from aldehyde reduction. Aldehyde consisted of using NEt3 as a ligand in various solvents
products that result from hydroformylation are quite (Table 1, entries 2–4). In all cases significant starting
often the desired products, however other types of material was recovered from the reaction. Increasing
compounds can be made by reacting the in-situ pre- the pressure of syngas only helped marginally
pared aldehyde; products such as amines,[6] indoles,[7] (Table 1, entries 5 and 6).
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Table 1. Optimization of alcohol synthesis at room tempera-
ture; varying gas pressure, solvents and ligands.
Table 2. Optimization of alcohol synthesis by reductive hy-
droformylation; varying solvents, temperature and ligands.
Entry Ligand
Solvent Pressure[b] Yield[c] [%]
1
2
3
4
5
6
Me2N
NEt3
NEt3
NEt3
Me2N
Me2N
N
2.76
6
9
–
8
8
9
Entry Ligand
Solvent b:l[d] Yield[e] [%]
[d]
2.76
2.76
1[b]
2[c]
3
Me2N
Me2N
Me2N
NEt3
U
THF
THF
THF
THF
THF
THF
PhMe
THF
12.4 36
12.2 53
9.6
5.0
7.9
6.1
6.8
6.9
–
82
31
48
57
40
54[f]
–
4.14
4
[a]
All reactions were performed in a glass liner inside
a metal autoclave using 0.96 mmol of styrene, 2.5 mol%
rhodium dimer complex, 10 mol% diamine ligand and
3 mL of solvent.
Combined pressures in MPa of the reagent gases (CO
and H2), the pressure of each gas was equal for all reac-
tions.
5
6
7
8
Me2N
Me2N
Me2N
Me2N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
[b]
9
MeHN
ACHTUNGTRENNUNG
10
Me2N(CH2)4NMe2
U
11.9 59
[a]
[c]
[d]
All reactions were performed in a glass liner inside
a metal autoclave at 1.38 MPa each of CO and H2,
0.96 mmol of styrene, 2.5 mol% rhodium dimer complex,
10 mol% diamine ligand, 608C reaction temperature
(unless otherwise stated) and 3 mL of solvent.
The reaction temperature was 388C.
The reaction temperature was 488C.
Branched to linear ratio determined by crude H NMR.
Isolated yield of branched and linear alcohols.
Yield for the reductive hydroformylation of styrene by
using 0.69 MPa each of CO and H2.
Isolated yield of branched alcohols.
Decomposition.
[b]
[c]
[d]
[e]
[f]
The next step in reaction optimization consisted of
1
increasing the reaction temperature beyond room
temperature (Table 2). Running the reaction at 388C
gave the desired product(s) with a branched to linear
ratio of 12.4, but only in 36% isolated yield. Increas-
ing the reaction temperature to 488C diminished the
branched to linear ratio slightly to 12.2 but increased
the isolated yield significantly to 53%. Finally an 82%
isolated yield was achieved by increasing the tempera-
ture another 108C to 608C, however, the branched to
linear ratio fell to 9.6. Additional ligands, solvents
and syngas pressures were screened to see if the
branched to linear ratio could be increased. In all
cases there was a lower branched to linear ratio and
isolated yield with the exception of using MeCN as
the solvent (entry 10), whereby the ratio of 11.9 was
attained in 59% yield.
Three background reactions were run to gain in-
sight into the reaction mechanism (Scheme 1). The
first background reaction subjected styrene to the hy-
droformylation–reduction sequence reaction condi-
tions in the absence of the tertiary diamine ligand.
This resulted in the production of the branched alde-
1
hyde, crude H NMR showed that there wasnꢁt any
Scheme 1. Background reactions run to gain an understand-
ing of the reaction mechanism.
branched alcohol, linear alcohol or linear aldehyde
produced. The second background reaction consisted
of subjecting styrene to a syngas atmosphere without
any rhodium catalyst, which resulted in recovered sty-
The reaction conditions were optimized to use
rene. The final background reaction had the branched 3.75 mol% of the rhodium dimer complex. However,
aldehyde subjected to the hydroformylation–reduc- the loading of the rhodium catalyst can be reduced if
tion sequence reaction conditions, which resulted in desired. As shown in Scheme 2, a 0.5 mol% loading
the production of the branched alcohol.
of the rhodium dimer complex can achieve a reasona-
2
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Synthesis of Alcohols via a Rhodium-Catalyzed Hydroformylation–Reduction Sequence
position. However, the starting material 1-methoxy-2-
propylenebenzene did not afford any product; only
starting material was recovered. This observation sug-
gests that coordination by ortho substituent groups
can interfere with the reaction. It is conceivable that
these coordinating groups can compete against the
olefin for a coordination sphere within the rhodium
complex thereby disrupting the hydroformylation
step. Extended aromatic groups also work well, such
as the para-phenylstyrene (1c) and the naphthalene
ring system (1j). Disubstituted olefins also work, how-
Scheme 2. Hydroformylation–reduction sequence reaction
after a reaction time of 64 h with 0.5 mol% dimer complex
loading.
ble 47% isolated yield of the branched alcohol in ever the yield is typically lower than for monosubsti-
64 h. The catalyst has a rather low turnover frequency tuted olefins. Indene afforded the alcohol (1g) in 62%
but it appears to proceed in relatively large turnover yield and 1-[(E)-prop-1-enyl]benzene gave the linear
numbers.
product (1k) in 44% yield. 1,2-Dihydronaphthalene
With optimized conditions in hand we evaluated also worked, but gave the alcohol (1l) in modest yield
the scope of the reaction (Figure 1). The reaction (35%) and with a branched to linear regioselectivity
yields a number of branched alcohols in very good of 3.7.
yields for a variety of substituted benzene ring sys-
tems. In all cases there were no traces of the olefin re-
duction product or the aldehyde product. The pres- Conclusions
ence of halogens does not effect the reaction, regard-
less of whether it is a bromine or chlorine atom or In summary, tertiary diamine ligands in conjunction
whether the position is ortho or para. Methoxy ether with RhClACTHNUTRGNE[UNG COD] dimer is an effective catalytic
groups do not affect the reaction in the meta or para system to directly prepare alcohols in good branched
to linear ratio, from aromatic styrene and related
compounds. Selectivity to alcohol products is excel-
lent.
Experimental Section
General Procedure
The glass liner that was used was charged with a stir bar,
flame-dried and allowed to cool. The cooled glass liner was
charged with 13.3 mg of [RhClACHTNUGTRENUNG(COD)]2 (0.054 mmol). In
a 1 dram vial was weighed the olefin (0.722 mmol) and
15.6 mg of N, N, N’, N’-tetramethylbutane-1,4-diamine
(0.108 mmol); 1 mL of freshly distilled MeCN was added
and the solution was charged into the glass liner containing
the rhodium complex. An additional 2 mL of freshly dis-
tilled MeCN were used to rinse out the 1 dram vial holding
the olefin solution. The glass liner was placed into the auto-
clave and screw capped with the metal cover and a pressure
gauge was attached. The contents of the autoclave were
purged five times with CO gas to 1.38 MPa each time and
pressurized to a final pressure of 1.38 MPa. The autoclave
valve was then closed to prevent any gas from being re-
leased. The CO gas line was cleared of CO gas and discon-
nected from the autoclave; an H2 gas line was then connect-
ed to the autoclave. The H2 gas line was purged 5 times and
then the H2 gas valve was placed on the “LOAD” position.
The valve to the autoclave was slowly opened and the pres-
sure on the autoclave was allowed to climb to 2.76 MPa
from 1.38 MPa, the autoclave valve was then closed. The H2
gas line was cleared of H2 gas and disconnected from the au-
toclave; the autoclave was then placed in a 608C preheated
oil bath, heated by a hotplate stirrer, and hooked up to
Figure 1. Substrate scope of rhodium-catalyzed hydroformy-
lation–reduction sequence with different aromatic olefins.
Reaction conditions: 0.72 mmol of aromatic olefin,
3.75 mol% of [RhClACHTUNTRGNEUNG(COD)]2, 15 mol% diamine ligand
(N,N,N’,N’-tetramethyl-1,4-diaminobutane), 1.38 MPa CO
and 1.38 MPa H2 gas, 3 mL of MeCN, 608C reaction temper-
ature, 22 hour reaction time.
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ˇ
a vent line. The contents of the autoclave were allowed to
stir in the oil bath overnight. After stirring for 21 h in the
heated oil bath the autoclave was removed from the oil bath
and allowed to cool for 30 min. After cooling the autoclave
was depressurized, the vent line was removed and the crude
reaction mixture was poured into a single-neck round-
bottom flask, the glass liner was rinse with dichloromethane
and the crude reaction mixture was concentrated and then
subjected to silica gel chromatography.
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Acknowledgements
We are grateful to the Natural Sciences and Engineering Re-
search Council for support of this research.
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Synthesis of Alcohols via a Rhodium-Catalyzed
Hydroformylation– Reduction Sequence using Tertiary
Bidentate Amine Ligands
5
Adv. Synth. Catal. 2012, 354, 1 – 5
Lawrence L. W. Cheung, Giuseppe Vasapollo,
Howard Alper*
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
asc.wiley-vch.de
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These are not the final page numbers!